Class-D audio amplifiers are switch mode amplifiers that switch at a high frequency to produce a rectangular waveform at the amplifier's output. Class-D amplifiers may be much more efficient than linear audio amplifiers, and as a result may employ smaller power supplies and eliminate heat sinks. Accordingly, class-D amplifiers may significantly reduce overall system costs, size, and weight relative to linear amplifiers of equivalent power.
Some class-D amplifiers use a pulse width modulator (PWM) to generate pulses that vary in width with the audio signal's amplitude. The pulses may switch output transistors of the amplifier at a fixed or variable frequency. Some class-D amplifiers may rely upon other types of pulse modulators, such as pulse density modulators. The rectangular waveform generated by the class-D amplifier is filtered to remove the high-frequency carrier waveform and reconstruct the audio waveform, which can be used to drive a speaker and produce sound.